A severe weather warning for the Bay of Plenty area on Monday has heightened fears that the stricken cargo vessel Rena, which is carrying 1,700 tonnes of fuel oil and 200 tonnes of diesel, will start to break up, with grim consequences for the local marine wildlife.

The fallout from the incident, which saw Rena run aground on a reef last Wednesday, is already being felt, with seven little blue penguins and two cormorants recovered and treated today at a centre in Tauranga.

However, this number is expected to rise to more than 200 in the coming days, with warnings that an escalation of the situation would have dire consequences for several species.

WWF New Zealand said it hoped the incident would not prove a "tragedy" for the region's marine wildlife, which includes bottlenose dolphins, orcas and beaked whales. Large baleen whales also migrate through the affected area.

Of particular concern is the New Zealand dotterel, an endangered shorebird.

"There's only 1,200 dotterels left due to coastal developments, so the last thing they need is their feeding ground contaminated," said Bob Zuur, marine advocate at WWF New Zealand.

"Little blue penguins are also very vulnerable as they swim through the oil. Fairy terns frequent the estuary and many northern hemisphere birds, such as godwits, that have migrated south for spring, are also under threat."

"New Zealand is known as the seabird capital of the world. We have about 85 different seabirds that breed here. It's breeding season now, so there are many birds, such as petrels, that are diving into the water to find food for their chicks.

"The oil makes it difficult for them to fly and there's a real risk they will ingest the oil when they preen, or pass it into their chicks.

"Should the vessel break up, we risk an international-scale incident. It's a huge amount of oil. I sincerely hope the it doesn't break up as the storm bears down on it."

It's estimated that up to 50 tonnes of oil has already been jettisoned into the sea. Radio New Zealand has reported that four of the 1,300 containers aboard Rena carry ferro-silicon, a hazardous substance which is flammable if it comes into contact with water.

More than 300 Defence Force personnel have been deployed to tackle the spill, along with specialists from Australia, the UK and the Netherlands.

The exclusion zone around the Rena has been extended to 2.8km today, with teams set to resume pumping oil off the damaged vessel. So far, just 10 tonnes of oil has been removed.

Humans, as well as marine wildlife, are also in danger from the spill, according to Maritime New Zealand.

The government agency has urged people not to touch the oil, which has started to wash up on the tourist-friendly Mount Maunganui beach, despite the efforts of volunteers to begin the clean-up operation.